Infections due to cytomegalovirus (CMV) are common in immunocomprised individuals and pulmonary infection due to this agent is a major source of morbidity and mortality. In pulmonary infections of the immunocomprised host, CMV is commonly isolated with another pathogen, leading to speculation that CMV itself may in some way predispose to subsequent infection. Despite this fact little is known about the effects of CMV infection on pulmonary defense mechanisms and the pathogenesis of CMV interstitial pneumonia remains undefined. Utilizing murine models of pulmonary and systemic CMV infection we intend to analyze the effects of this agent on murine pulmonary antimicrobial activity and defense mechanisms. Moreover, we will characterize in vitro interactions between MCMV and alveolar macrophages and determine the impact of CMV infections on macrophage function. Attempts to correlate in vitro observations with alterations of in vivo clearance mechanisms will greatly extend our understanding of CMV infection of the lung and its interaction with host defense mechanisms.